Two lamp type high power factor fluorescent lamp device



Sept 17, 1957 TORU ASANQ 2,806,981

TWO LAMP TYPE HIGH POWER FACTOR FLUORESCENT LAMP DEVICE Filed June 15, 1955 2 Sheets-Sheet 1 Sept 1957 TORU ASANO 2,806,981

TWO LAMP TYPE HIGH POWER FACTOR FLUORESCENT LAMP DEVICE Filed June 15, 1955 2 Sheets-Sheet 2 United States Patent ()ifice 2,806,981 Patented Sept. 17, 1957 TWO LAMP TYPE HIGH POWER FACTOR FLUORESCENT LAMP DEVICE Toru Asano, Setagaya-ku, Tokyo, Japan, assignor to The Governor of Tokyo Metropolitan Ofiice, Tokyo, Japan Application June 15, 1955, Serial No. 515,725 Claims priority, application Japan December 5, 1949 2 Claims. (Cl. 315-96) The present invention relates to an improved circuit for the operation of two fluorescent lamps.

In the present state of the art, hot cathode fluorescent lamps in commercial operation require the use of a separate transformer such as step-up transformer or autotransformer and also so-called starting switch or a starting lamp to obtain a sure starting.

However, cost of the lamp device equipped with said elements will be raised and said device requires troublesome treatment.

Therefore, it is an object of the present invention to provide a circuit for the operation of two hot cathode fluorescent lamps which results in instant starting and uniform operation, without employing a step-up transformer and starting switch or starting lamp which is liable to be damaged, when the lamps are connected to ordinary commercial power lines such as 220 volts, 60 cycle A. C. or 120 volts, 6O cycle A. C. Another object of the present invention is to provide a circuit for the operation of two hot cathode fluorescent lamps which produces a fiickerless illumination. Said objects and other objects of this invention have been accomplished by an improved circuit for the operation of two fluorescent lamps which is hereinafter more fully described and illustrated in the accompanying drawings, wherein:

Figs. 17 are seven kinds of circuit diagrams of the discharge device composed of two fluorescent lamps, which should be improved by this invention.

' Fig. 8 is a circuit diagram of an example of this invention.

' Fig. 9 is a circuit diagram of another example of this invention.

Fig. 10 is a vector diagram of the voltages to be distributed to various parts of the circuit at the starting instant.

In all figures, the same parts are shown by the same symbols and numerals.

Referring to Figs. 1-9, the discharge device is composed of the first and second hot cathode fluorescent lamps 3 and 5, said lamp 3 being composed of an elongated discharge tube filled with a suitable gas or vapour in the known manner and having hot cathodes 4'and 8 enclosed at opposite ends of said tube and said lamp 5 being composed of an elongated discharge tube similar to the like to said tube of lamp 3 and having hot cathodes 6 and 7 enclosed at opposite ends of said tube.

Referring to the circuit shown in Fig. 1, first terminal of the cathode 4 of the lamp 3 is connected to one side 1 of the power lines through an inductance L1 and second terminal of the cathode 7 of the lamp 5 is connected to said side 1 through an inductance L2. The first terminal of the cathode 8 of the lamp 3 is connected to other side 2 of the power lines through an inductance L: and the second terminal of the cathode 6 of the lamp 5 is connected to said side 2 through an inductance L4;

Between the second terminal of the cathode 4 and the first terminal of the cathode 6 is connected a capacitive impedance Z01 composed of an inductance and capacitance. Between the first terminal of the cathode 7 and the second terminal of the cathode 8 is connected a capacitive impedance Z02 composed of an inductance and a capacitance. The values for L1, 201 and L4 are so selected as to be resonant at line frequency in their series condition and the values for L2, Z2 and L3 are so selected as t be resonant at line frequency in their series condition.

The operation of the circuit in Fig. l is as follows. Upon connection of the circuit to both sides of the line, large currents pass parallelly through a circuit composed of the inductance L1, cathode 4, impedance Zcl, cathode 6 and inductance L4; and through another circuit composed of the inductance L2, cathode 7, impedance Zc2, cathode 8 and inductance L3, whereby said cathodes are effectively heated. On the other hand, as the values of said elements L1, Zcl, L4 and L2, Z02, Ls are, respectively, so selected that they are resonant at line frequency, relatively large voltages suflicient for starting of the lamps 3 and 5 occur between the cathodes 4 and 8 and between 7 and 6, so that both of the lamps 3 and 5 are instantly brought in discharge condition. Immediately the lamps discharge, it destroys the greater parts of the resonant effect of said both resonant circuits which are operated in parallel condition. And the effects of the impedance Zcl and Z02 are dropped out of said parallel circuits due to their high impedance in relation to the negative resistance characteristics of the discharge lamps. After said starting, only slight currents due to potential difierences between the cathodes 4 and 8 and between the cathodes 6 and 7 flow through the lamps 3 and 5 and said lamps operate in stable and parallel condition.

The circuit shown in Fig. 1 may be modified as shown in Figs. 2, 3, 4 and 5, wherein the symbols L1, L2, L3, L4, L5 and Le are inductances and Z61, Z02, Z03 and Zc are capacitive impedances.

Selection of the values of various inductances and capacitive impedances in the parallel circuits which are to be formed at the starting and operations of the circuits shown in Figs. 2, 3, 4 and 5 are similar to those in the circuit described in connection with Fig. 1, so that descriptions relating to said facts are omitted.

According to said circuits shown in Figs. 15, capacity of the condenser to be used in the capacitive impedance should be relatively large, whereby cost of the circuit becomes high.

Said disadvantage can be avoided by the circuits as shown in Figs. 6 and 7, wherein L7 and L8 are inductances and Zc5 is a capacitive impedance and the values of said inductances L7, L3 and the capacitive impedance Z5 are so selected so as to be resonant at line frequency in their series condition.

' Upon connection of the circuit in Fig. 6 to both sides 1 and 2 of the lines, current passes through a series circuit composed of the cathode 4, inductance L7, cathode 7, impedance Z05, cathode 8, inductance L3 and cathode 6, whereby said cathodes are heated. As the values of said elements L7, L8 and Z05 are so selected that they are resonant at line frequency, relatively large voltages sufficient for starting of the lamps 3 and 5 occur between 5 and cathode 6. And the effect of is dropped out of circuit due to its inductance L7, cathode 7, dischargethe negative resistance char- After said starting,

high. impedance in relationto acteristics of the discharge lamps. only slight current due the cathodes 7 and 8 flows through the impedance Zc and the lamps 3 and 5' operate in stable and parallel condition.

The. circuit shown inv Fig. 7 is completely equal to that in Fig. 6 except that in Fig. 7, theinductance corresponding to the, inductance L3 in Fig. 6 is divided, into two inductances L's and L9, said inductance L's being connected between the. first terminal of the second cathode of the lamp 3 and the first terminal of the second cathode of .the lamp 5. and said inductance L9 being connected between the second terminal of the second cathode of the lamp 5 and the side 2 of the lines. Said inductance L9 provides means for limiting the currents of both lamps 3 and 5 when, line voltage becomes accidentally over voltage.

According to the circuits in Figs. 6 and, 7, there is an advantage that the value of capacitance to be used for the capacitive impedance Z05 can be selected so as to be about /2 of that of the capacitive impedance to be used for the circuits shown in Figs. 1-5, but parallel currents passing through the lamps 3 and 5 during their normal operations are both lagging currents, so that power factor of the lamp device is relatively low and also flicker is liable to occur. 1 7

Therefore, this invention is proposed to avoid all of said disadvantages in such circuits for the operation of two fluorescent lamps as described in connection with Figs. 1-7.

According to this invention, the circuit is composed of a source of alternating current of a predetermined frequency, a first lamp composed of a discharge tube and first and second cathodes enclosed at opposite ends of said tube, first terminal of said first cathode being connected to one side of said source, a second lamp composed of a discharge tube and first and second cathodes enclosed at opposite ends of the aforesaid tube, second terminal of said second cathode being'connected to other side of said source, an inductance connected between the second terminal of the first cathode of the first lamp and the second terminal of the first cathode of the second lamp, another inductance connected between the first terminal of the first cathode of the second lamp and the second terminal of the second cathode of the first lamp, and a capacitive impedance connected between the first terminal of the second cathode of the first lamp and the first terminal of the second cathode of the second lamp, said two inductances and capactive impedance having such values as to provide substantial resonance at said predetermined frequency in their series condition.

This invention will be more clearly understood from the description taken in connection with the circuits illustrated in Figs. 8 and 9.

Referring to the circuit illustrated in Fig. 8, one terminal of the cathode 4 of the first fluorescent lamp 3 is connected to one side 1 of the power lines and the other terminal of said cathode is connected to the opposite side 2 of said power lines through inductance L10, cathode 7, inductance L11, cathode 8 of the first lamp 3, capacitive impedance Zc6 composed of an inductance L and a capacitance C, and cathode 6 of the second fluorescent lamp 5. The values for L10, L11 and Zea are so selected as to be resonant at line frequency. Without limitation, and merely by Way of example, the following values for inductances, capacitance and capacitive impedance are given for the circuit of Fig. 8 when operating on a line source of 50 cycle and 200 volt, output of each lamp in said circuit being 40 watt.

L1o-0.75 henrys, ohms (coil is wound on an iron core).

L11-0.75 henrys, 20 ohms (coil is wound on an iron core). 7

to potential difierence between Zcevalues of coil0.75 henrys, 20 ohms. Capacity of the condenser4 micr'ofarads.

When each of said lamps are 20 watt, it is preferable to adopt the following data.

L1o0.6l henrys, 20 ohms.

L110.55 8 henrys, 20 ohms.

Zea-values of coil-O.93 henrys, 20 ohms. Capacity of the condenser6 microfarads.

, L10, cathode 7, inductance L11, cathode 8, capacitive 1mpedance ZcG and cathode 6, whereby said cathodes are effectively heated. As the values of said elements L10, L11 and Z06 are so selected that they are resonant at line frequency, relatively high voltages sufficient for starting the lamps 3, and 5 occur between the cathodes 4 and 8 between the cathodes 6 and 7, so that both of the lamps 3 and 5 are instantly brought in discharge.

ccurrence of said temporary high voltage at the start-. ing in the'circuit in Fig. 8 can be proved by the 'vector diagram as shown in Fig. 10.

When line voltage, current passing through said series resonant circuit, angular velocity of line voltage, re sistance drop in the cathode 4, reactance voltage of the inductance L10, resistance drop in the cathode 7, reactance voltage of the inductance L11, resistance drop in the cathode 8, reactance voltage of the inductance L, reactance voltage of the capacitance C and resistance drop in the cathode 6 are, respectively, shown by E, I, :0, R41, jwLroI, R71, jwLuI, RaL J' LI,

and R61, the vector diagram as shown in Fig. 10 is obtained.

As will be understood from said diagram, the voltages between the cathodes 4 and 8 and between the cathodes 7 and 6 become E1 and En, respectively, said voltages being relatively higher than the voltage E.

Immediately the lamps discharge, it destroys the greater parts of the resonant efiect between the elements L10, L11 andZce allowing formation of two current circuits, the one thereof being composed of the line side 1, cathode 4, discharge tube of the lamp 3, cathode. 8, capacitive impedance Zcfi, cathode 6 and line side 2 and the other being composed of the line side 1, cathode 4, inductance L10, cathode 7, discharge tube of the lamp 5, cathode 6 and line side 2. And the effect of the inductance L1; is efi ectively eliminated from the circuit due to its high impedance in relation to the negative resistance characteristics of the discharge lamps. After said starting, only slight current due to potential difference between the cathodes 7 and 8 flows through the inductance L11 and the lamps 3 and 5 operate in stable and parallel condition.

In said stable operations of the lamps, the current passing through the lamp 3 is leading current and the current passing through the lamp 5 is lagging, so that power factor of this lamp device is very high such as %1.0.0% and flicker due to stroboscopic eflect does not occur, because there is a relatively large phase difference between the currents in the lamps 3 and 5.

In the circuit illustrated in Fig. 8, the inductance L may be divided into two inductances, the one part thereof being connected as shown, and the other part between one side 1 of the lines and the cathode 4 thereby resulting in operation thereof like theinductance L9 in Fig. 7.

The circuit illustrated in Fig. 9 is similar to that in Fig. 8 in their constructions and operations except that the inductance L in Fig. 8 is divided into two parts L12 and L13, one part thereof may be connected between the line side 2 and the cathode 6 to make it operate as the inductance L9 in Fig. 7.

Furthermore, in a practical embodiment of the lamp arrangement according to the present invention, it is preferable, as is shown by broken lines in Fig. 9, to electrostatically insulate the metallic casing 9 from both the lamps 3 and 5, which are electrostatically insulated from each other. The metallic casing 9 is connected to the junction of the inductance and the capacitance of the impedance Zea through a high resistance 10 and a capacitance 11 in order to assist the starting. In the practical embodiment of the arrangement according to Fig. 9, of which the constants are as stated hereinabove, the suitable values of capacitance 11 and resistance 10 are 0.01 f. and 250 K ohms, respectively.

According to this invention, as will be understood from the above description, a very excellent circuit having following effects will be obtained.

(a) All cathodes of two fluorescent lamps are connected in series to a resonant circuit and a relatively large current flows through said circuit at the starting, so that every one of both fluorescent lamps starts instantaneously by relatively low commercial line voltage such as 120 volts or 220 volts Without the provision of starting devices such as transformer or starting switch, because both cathodes of each lamp are heated with large resonance current and relatively high voltage is applied to each fluorescent lamp at the starting.

(b) There is a phase difierence of about 90 between the discharge currents of the fluorescent lamps, so that an excellent flickerless lamp device will be obtained.

I have shown various embodiments, but various changes can be made therein without departing from the principle of the invention. This invention may be used for cathode fluorescent lamps.

What I claim as my invention is:

1. A circuit for the operation of two fluorescent lamps comprising a source of alternating current of a predetermined frequency, a first lamp composed of a discharge tube and having first and second cathodes enclosed at opposite ends of said tube, a second lamp composed of a discharge tube and having first and second cathodes enclosed at opposite ends of said second lamp tube, each of said cathodes being provided with first and second terminals, the first terminal of the first cathode of said first lamp being connected to one side of said source, the second terminal of said second cathode of said second lamp being connected to other side of said source, a first inductance connected between the second terminal of the first cathode of the first lamp and the second terminal of the first cathode of the second lamp, a second inductance connected between the first terminal of the first cathode of the second lamp and the second terminal of the second cathode of the first lamp, and a capacitive impedance connected between the first terminal of the second cathode of the first lamp and the first terminal of the second cathode of the second lamp, said inductances and capacitive impedance having such values as provide substantial resonance at said predetermined frequency.

2. A circuit for operating two hot cathode fluorescent lamps according to claim 1, in which the first inductance is divided into two parts, one of said parts being connected between one side of the source and first terminal of the first cathode of the first lamp and the other part being connected between the second terminal of the first cathode of the first lamp and the second terminal of the first cathode of the second lamp.

References Cited in the file of this patent UNITED STATES PATENTS 2,314,311 Karash Mar. 16, 1943 

